As V1 is not allowed to be lower than Vmcg...
Full power delays the decision point to a higher speed because in the go scenario the higher thrust can still accelerate the aircraft to flying speed in the shorter remaining runway length.
Full power allows for a decision point with a higher speed because in the stop scenario with the higher thrust it will be reached sooner during the roll, leaving more distance remaining to kill the increased energy (Ek = 1/2*m*v*v).